This invention relates in general to a liquid-ring rotary compressor and more particularly to a control disc in such a compressor for at least partially determining the output pressure thereof.
A liquid-ring rotary compressor comprises a machine housing generally with a substantially cylindrical compression chamber, a pair of bell-shaped support plates at opposite ends of the housing and an impeller located in the compression chamber. The impeller has a shaft journaled at opposite ends in the support plates or end bells and a multiplicity of substantially radial blades defining a multiplicity of blade chambers rotable within the housing. A control disc disposed between one of the bell-shaped support members and the housing is provided with a sickle-shaped suction slot and a sickle-shaped pressure slot, the pressure slot having a substantially radial leading edge. The support member juxtaposed to the control disc has a gas intake and a gas outlet communicating with the blade chambers via the suction slot and the pressure slot, respectively. The control disc is further provided with channels or ducts for enabling the passage of liquid (e.g. water) into and out of the compression chamber and with a multiplicity of ancillary pressure openings distributed in an arc-shaped region located circumferentially in front of the pressure slot, as determined by the direction of rotation of the impeller. The arc-shaped region extends in a radial direction beyond the outer end of the leading edge of the pressure slot, while the pressure openings have, in the circumferential direction, dimensions matched to the thickness of the impeller blades.
Liquid-ring rotary compressors described in Siemens price list P 20, Part I., July 1964, pages 4 and 5, and Siemens publication E725/1013, "Vacuum Pumps and Compressors, Siemens System ELMO-F" ("Vakuumpumpen und Verdichter, Siemens System ELMO-F"), have a circulating water feed or pressurized liquid passage behind the suction slot, relative to the direction of impeller rotation, for admitting the gap-sealing liquid (e.g. water) to the compression chamber. The pressure outlet in the control disc is constituted by the sickle-shaped pressure slot together with holes in the arc-shaped region preceding the pressure slot. The size of the pressure outlet, and in particular of the pressure slot, determines the ratio of the final or outlet pressure to the suction or inlet pressure. Thus the beginning of the pressure outlet, relative to the direction of rotation of the impeller, must be adapted to the desired pressure ratio. To this end the position of the inner contour of the housing relative to the pressure outlet must be adjusted. The hole of the arc-shaped area which are situated in the output pressure region allow the compressed gas to penetrate from the front side of the control disc, i.e. the side facing the impeller, to the back side of the control disc more easily than the holes farther removed from the output pressure region, since the liquid located on the back side of the control disc closes off the holes on which less pressure acts on the front side, so that in practice a sort of liquid valve action occurs.
For larger pressure ratios a plate valve is frequently provided on the back side for aiding the action of the liquid valve.
Because the diameter of the holes must be adapted to the thickness of the blades and a ratio of a hole diameter to blade thickness of 1.2:1 should not be exceeded, the flow velocity must not fall below a limit and corresponding flow losses must be tolerated. The ratio of hole diameter to blade thickness is chosen in view of detrimental back flow via hole to hole from one blade chamber to another, since excessive back flow cancels possible efficiency improvement by a decrease of the flow losses due to smaller flow resistances. Increasing the number of holes for the purpose of reducing the flow velocity is possible neither in the radial direction nor in the circumferential direction, since in the former case the rotating liquid ring is adversely affected and in the latter case the pressure ratio would be reduced.
An object of this inventon is to achieve in a liquid-ring compressor a reduction of the required power consumption and an improvement in efficiency for pressure ratios varying over a wide range, while eliminating the need for a housing adjustment.